Fraction Calculator Plus
The app puts 3 keypads on the screen so that you can directly enter the integer portion, the numerator and the denominator.
1 15/32 + 3 5/8 = 5 3/32
If you want, you can tap a button to see a scratchpad type screen showing a "handwritten" breakdown of the steps required to get the answer. That screen also shows you the decimal version of the answer, e.g. 5.09375